6LR61 battery

The combination of improved electrolyte and process optimization has significantly improved the suppression of high-temperature flatulence in soft-pack 6LR61 battery.

With the continuous development of new energy 6LR61 battery, soft-pack 6LR61 battery with aluminum plastic films as outer shells are widely used in power industry, consumer electronics and other products. Due to actual use, affected by the use environment, season, regional climate, etc., high temperatures will inevitably occur, which can easily lead to flattening of soft-pack 6LR61 battery and greater damage to electrical performance. Through the evaluation of electrolyte and process optimization, it was determined that the combination of improved electrolyte with 3% VC content additive and process optimization can significantly improve the suppression of high-temperature flatulence and sustained damage to electrical properties of soft-pack 6LR61 battery.

1 experiment

1.1 Formulation and design

Positive electrode (oil system): lithium cobalt oxide: conductive agent (SP): binder (PVDF-HSV900) = 96:2:2 (mass ratio); negative electrode (water system): graphite (Ningbo Shanshan FSN-4): Thickener (CMC): Binder (SBR) = 95.5: 1.5: 3.0 (mass ratio); Separator: 16μm Celgard separator; Electrolyte: Guangzhou Tianci. According to the above formula and design, it is rolled and assembled into a 494147 model soft-packed square battery.

1.2 Trial production of improved electrolyte batteries with different contents of VC additives

Use the Tianci TC-E233H model electrolyte, add 0%, 1.5%, 3%, and 4.5% VC additives respectively to make it into four electrolytes. Inject the electrolyte into the 494147 model soft-packed square battery to form A, Four program batteries, B, C, and D, are used for subsequent testing (Program A is the comparison group). Note: Process steps after liquid injection: ① Leave at room temperature for 8 hours → ② Formation → ③ Leave at 40°C for 24 hours → ④ Degas and edge seal → ⑤ Flat press → ⑥ Divide the volume.

1.3 Trial production of process optimization batteries

The process flow after injection of soft-pack lithium battery is: ① Let it stand at room temperature for 8 hours → ② Formation → ③ Let it stand at 40℃ for 24 hours → ④ Remove air and seal the edges → ⑤ Flat press → ⑥ Divide the volume; optimize the process of step ① in 4 groups The remaining steps remain unchanged, Group 1: Leave at room temperature for 8 hours (comparison group); Group 2: Leave at 60°C for 8 hours; Group 3: Leave at 85°C for 8 hours; Group 4: Leave at 100°C for 8 hours; for Follow-up testing (the electrolyte adopts plan A, that is, adding 0% VC).

1.4 Trial production of the best solution battery

Based on the optimal percentage content of VC electrolyte obtained in Section 1.2 and the optimal resting temperature in Section 1.3 above, the optimal solution battery was remade for subsequent testing and evaluation.

2Experiments and conclusions

2.1 Experiments on improved electrolyte batteries with different contents of VC additives

Experimental steps: Take the batteries of the four schemes A to D in Section 1.2, ① test the initial capacity and thickness; ② fully charge; ③ place in an 85°C thermostat for 48 hours; ④ take out and cool to room temperature, and re-test the capacity and thickness; Repeat from ② to ④ until all the flatulence is cut off and test; compare the period, capacity loss rate, and expansion rate of the first flatulence among the four plans. As can be seen from Table 1, Schemes C and D have strong resistance to high-temperature flatulence, and flatulence did not appear until they were exposed to 85°C for 48 hours in the third week. As can be seen from Figure 1, Schemes C and D have higher cell expansion rates after weekly high-temperature shocks. Compared with Schemes A and B, it is much smaller; as can be seen from Figure 2, the capacity loss of the battery with VC added to the electrolyte is greater than that of the battery without VC, and as the amount of VC added increases, the capacity loss also increases.

VC improves the ability to resist high-temperature flatulence, but the loss capacity after high-temperature impact is also relatively increased. This feature can be explained from the characteristics of VC itself: VC is a new organic film-forming additive and overcharge protection additive for lithium-ion batteries. It has good The high and low temperature performance and anti-inflation function can improve the battery capacity and cycle life. When the battery core is stored and stored at a high temperature of 85°C, the negative SEI protective film will inevitably be damaged and VC will be repaired to form a film. If there is no VC in the electrolyte, the film will continue to be damaged, and the negative electrode carbon will react with the electrolyte. The gas produced by the reaction causes the cell to bloat; if there is VC, the VC will continue to repair the damaged SEI film to prevent the negative electrode carbon from reacting with the electrolyte to produce gas. However, the repair process will inevitably consume the effective lithium in the electrolyte. , resulting in irreversible capacity loss and increased capacity loss. Based on the results in Table 1, Figure 1 and Figure 2, Plan C (adding 3% VC to the Tianci TC-E233H model electrolyte) is the best plan for the experiment in Section 2.1.

2.2 Experiments on process optimization of batteries

Experimental steps: ① Test the initial capacity and thickness of the 4 sets of batteries in Section 1.3; ② Fully charge; ③ Place in an 85°C thermostat for 48 hours; ④ Take out and cool to room temperature, and retest the capacity and thickness; from ② to ④ Repeat until all the flatulence is cut off and test; compare the period and volume of the first flatulence among the four plans. Based on the results, Group 3 (after injecting the liquid, let it stand at 85°C for 8 hours in the oven, and then put it on the cabinet to form) is the best solution for the experiment in Section 2.2. Standing at high temperature for 8 hours after liquid injection is beneficial to the battery's ability to resist high-temperature flatulence in the later period. Although flatulence occurred in the second week of 2, 3, and 4, groups 3 and 4 were more beneficial in comparison; as can be seen from Figure 4, Note After the liquid was left to stand at high temperature, the average capacity of the battery was reduced, and the capacity of the fourth group was seriously low. After the liquid was injected, the process optimization of changing the room temperature to high temperature standstill improved the ability to resist high temperature flatulence, but it also caused The capacity becomes low. Because the SEI protective film is not formed on the negative electrode of the battery before formation after liquid injection, under these conditions, some components in the electrolyte will slowly react with the negative electrode to produce gas, changing the normal temperature to high temperature, which can accelerate the catalysis of the side reaction of the gas-generating substances. process, so that it can react as much as possible to avoid reacting and producing gas during the later thermal shock of the 85℃ 48h cycle, thereby causing flatulence. Due to accelerated catalysis at high temperatures, side reactions increase as the temperature increases, and the irreversible capacity increases. Therefore, the average capacity continues to decrease after volume division in the later stage. When the temperature is 100°C, other components of the electrolyte may also be damaged by heat. Decompose, and the capacity will be seriously low. If the temperature continues to increase, it will easily lead to the failure of the electrolyte, and the electrical performance of the battery will deteriorate sharply in the later period.

2.3 Experiment on the best solution battery

Add 3% VC additive to the Tianci TC-E233H model electrolyte. After the battery is wound and injected, ① let it stand at 85℃ for 8 hours → ② form → ③ let it stand at 40℃ for 24 hours → ④ remove the air and seal the edges → ⑤ flat press → ⑥ minutes Capacity; that is, combining the best solutions in the experiments in Sections 2.1 & 2.2, a battery is made, and after repeated thermal shock at 85°C for 48 hours, the cycle of the first flatulence, capacity loss rate, and expansion rate are evaluated; and then the new battery is obtained after dividing the capacity. , after repeated shocks at 85℃ for 48 hours, the number of shock weeks must be the week before the first flatulence (for example: assuming the first flatulence occurs for the fifth time, then take the fourth week), and finally evaluate the approach after thermal shock at 0.5C Circulation performance before the edge of flatulence. It can be seen from Table 3 that the new battery made by combining the best solutions of the experiments in Sections 2.1 & 2.2 has stronger high temperature resistance and can ensure that it will not be flatulent after being repeatedly impacted for 3 times at 85°C for 48 hours, and the expansion rate is also 1% to 5 Within %.

3Conclusion

(1) The electrolyte VC additive has a significant inhibitory effect on battery high-temperature bloating, and adding 3% to the Tianci TC-E233H model is the optimal value;

(2) Optimize the manufacturing process and optimize the 8 hours of standing at room temperature after injection to 85 hours of standing at 85°C. This will maximize the reaction of the material components in the electrolyte that react with the negative electrode to produce gas, and avoid re-reaction during thermal shock in the later stage. gas, thus causing flatulence, and also has a significant inhibitory effect on the high-temperature flatulence of the battery;

(3) By combining the method of "adding 3% VC to the TC-E233H type electrolyte and injecting the liquid, then leaving it at 85°C for 8 hours before forming", the soft-packed square lithium battery is resistant to high temperature thermal shock It has stronger ability and can reach 85℃ for 3 times for 48 hours without flatulence. The battery still has excellent cycle performance of >85% after being subjected to 3 thermal shocks at 0.5C for 300 cycles.

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